Neisseria gonorrhoeae (the gonococcus) is a human specific pathogen that is the causative agent of the disease gonorrhea. Type IV pili are a major virulence factor for many bacterial pathogens, including the pathogenic Neisseria, and these dynamic fibers promote adherence, motility, and genetic transfer. Extension and retraction of the Type IV pili relies on a complex envelope-associated secretion apparatus. We plan to investigate three novel aspects of gonococcal Type IV pilus assembly and function. We will determine whether the N-terminal domain of the pilin protein contributes to gonococcal pilus functions, and identify the protease that separates the N-terminal domain from the secreted S-pilin form of pilin. We will also determine whether there are different classes of pilus assembly apparatuses defined by function. Our second objective is to investigate the role of the Mpg protease in pilus expression. We will define interactions between Mpg, peptidoglycan and a subset of pilus assembly factors in the periplasm. We will test the hypothesis that these components form a complex, whose activity is dependent on Mpg's activity against peptidoglycan, which is responsible for keeping the pilus in an extended state. These studies reveal unique mechanisms required for gonococcal Type IV pilus expression and function during pathogenesis.